Machine for rolling screw threads



se nso, 1941. G.GOULb 2,257,234

MACHINE FOR ROLLING SCREW THREADS Filed Jan. 11, 1940 2 Sheets-Shegt 1 I I. l

Sept. 30, 1941. G. GOULD 2,257,234

MACHINE FOR ROLLING SCR EW THREADS I Filed Jan. 11, 1940 2 Sheets-Sheet 2 ATTORNEY timing means and enables successive work-pieces v Patented Sept. 3( 1941 'UNITED STATES PATENT OFFICE 2,257,234 I MACHINE FOR ROLLING SCREW THREADS George Gould, Birmingham, England. assignor to Wolseley Motors land Limited. Birmingham, Eng- Applicationt'lamlary 11, 1940, Serial No. 313,305 In Great Britain December 4, 1939 401mm. (case-s). i

This invention relates to machines ior rolling screw-threads, said machines being of the kind comprising two geared-together power-driven threading rolls mounted to revolve about parallel axes, the work-piecebeing fed and rolled 5 between them by being passed along a plane nor 'mal to that joining the axes of the rolls, and

the said rolls being so spaced apart that the shortest distance between their adjacent periphfinished eter i0 work-piece being inserted between the rolls atlti any instant. p I

A further object is to ensure that the correct tracking or angular relationship 01 the threads of the respective rolls is constantly maintained.-

It is usual in thread-rolling appliances to maize so the .pitch diameter of the rolls a whole number multiple of the diameter of the pitch diameter of the finished work-piece, and in order to prcduce the correct-spiral angle the rolls are do with a plurality .of threads or starts corren according to the invention, a machine" sponding with the said multiple. It is known to employ rolls which are of exactly equal diametc: and which are driven at diiierent rotational speed'sto cause the work-piece to be fed or traversed through the pass or space between the rolls,

but with this known machine the threads. of "one.

roll-are in correct relationship with those of the other roll at certain intervals only, and as the insertion of the work-piece must coincide with such intervals, successive work pieces can only be the supply. of the work-pieces to the rolls.

The present invention obviates the use of such tobeinserted at any moment.

, In connection with the relationship of the threads of the two rolls, it should be explained that, for producing the normal single type of thread, the threads of one roller. on the plane Passing through the axes of the two rolls, must threads on the other roll, but owing to the spiral angle of the threads of the two rolls, this relao tionship oi the threads alters as the plane of intersection is moved away from the central plane.

' In practice, that portion of the work-piece on which the thread is to ,be formed isginitially made to a diameter "appreciably greater than that at 55 Figure 2 is a diagram showing the maintained the root of the finished thread, this diameter being usually equal to the pitch diameter; and therefore, when the work-piece is in position for commencing the rolling operation, contact of the work-piece with the rollers is made at points situs in a plane at an appreciable distance from the central plane. Thus, as explalnedabove. the thread and gap relationship or the threads on the two rolls cannot, at one and the same time,

be correct at these points'and also on the central plane. The present invention ensures that the threads oi one roll are always opposite to the gaps between the threads 01 the other roll at all times a 21-; the rolling operation, namely, not only at the commencement of the operation, but also throughout the operation up to the finish oi the ending. According to the invention, a. machine for roll-' screw-threads, of the kind referred to, comprises two positively-driven threading rolls both son at the same rotational speed and in the direction-but having 'diilerent diameters such as to cause th work-piece to be fed or drawn between the rolls,

for rolling screw-threads provided with positively=driven threading rolls having diflerent peripheral has one of the rolls fre to slide axially relatively to the other roll, whereby, at one end of its axial travel, it may havea correct thread-and-gap relationship with the other roll .10: the commencement of the rolling operation,

and, as the work-piece progresses towards the centre plane 01 the rolls, it may slide endwise, due to the tracking of the-threads, to maintain such correct relationship throughout the oper- 'ation'. The slidable roll. may be acted upon by a spring which maintains it in an initial position for correct thread-and-gap relationship at the 40 commencement of the operation, the roll moving axially against the action or the spring during the progression of the work-piece towards the centre plane oi the rolls. The initial position oi *the slidable roll lot the commencement of the operation may be determined by an adjustable stop with which one end 01 the roll co-operates.

- Figure 1 of the accompanying drawings is a tic end view of a thread-rolling machine in accordance withthis invention showins in full lines the work-piece at thecommencement oi the operation, and, in broken lines, the position of the said work-piece at the end of the operation.

' diameter gear-wheels 6, 1, respectively, both these wheels meshing with a single driving gear-wheel 8 rotated from a suitable source of power, whereby both rolls I, 2; are driven at similar rotational speeds. The roll I is fixed upon its spindle 3, but, for the purpose hereinafter described, the roll 2 is slidably keyed or feathered to the spindle 4, as by'a key 9 engaging a key-way III, with clearances at I I, II, between the ends of the roll and the supporting parts of frame 5, so that the said roll can move axially on the spindle. The two rolls I, 2, are.not of exactly the same diameter, the diameter of one being slightly greater than that of the other, but the difference in the two diameters (which difference cannot very well be indicatedin the drawings) need only be suflicient to ensure that the work-piece I2 will be drawn into the pass or space between the rolls, due to the slight difference in peripheral speeds of the rolls created by the difference in diameters. The

time required for the threading operation on the work-piece, namely, while it is being drawn and an adjustable stop I, the latter being adjusted so that, in the plane at A, A, the threads of one roll are exactly opposite to the gaps rxspaces between the threads of the other roll. In the said plane through the points A, A, this correct thread and gap relationship is maintained continuously throughout the rotation of the rolls and over the entire length of their peripheries, since the rotational speed of thetwo rolls is the same. The work-piece can thus be inserted between the rolls at any instant. 'This constitutes an important advantage compared with the known threading rolls which are driven at'diflerential speeds, as in that case the correct thread-,and-gap relationship only occurs intermittently.

As hereinbefore explained, if the rolls had no relative axial movement permitted them, it would only be possible for correct tracking to be obtained. at one position of the work-piece during its traverse between-,the rolls, for example, at position A, A. However, the fact that the roll 2 is capable of moving axially on its spindle under the control of the spring plunger I4, en-

rolled from the commencing position shown at A A, A, Figure 1, to the finished position at B, B, is controlled by this difference in peripheral speeds. For a work piece of comparatively soft material, however, the difference may be greater than that for a harder material, thereby shortening the time required for the rolling operation.

The pitch diameters of the said rolls I, 2, are approximately a whole number multiple of the pitch diameter of the thread to be rolled on the work-piece, and in order to produce the correct spiral angle the rolls are made with a number of threads or starts which is the same as said ,multiple.

For producing the normal single type of thread it is necessary that, on the plane passing through the axes of the rolls I, 2, namely, at B, B, Figure 1, the threads of one roll should be exactly opposite to the gaps or spaces between adjacent threads on the other roll, as indicated in Figure 2. This relationship alters, however, as the plane of intersection is; moved away from the central plane.

tact of the work-piece with the rolls is made at points situated at an appreciable distance from the central plane. Thus, the thread and gap relationship of the two rolls cannot, at one and the same time, be correct on the planes at A, A,

and B, B. The correct relationship at the commencement of the operation, namely, when the work-piece is at A, A, can be obtained by setting the rolls in a suitable relative axial-position. In the example ,shown in Figure 3, this may be achieved by moving the axially-slidable lower roll 2 endwise along its spindle 4, bymeans of a spring-loaded plunger I3, until it is arrested by sures the rolls being automatically maintained in correct tracking relation throughout the move- .ment of the work-piece between them, that is to say, at every plane at which the work-piece is in contact with them at different stages of the rolling operation.

Thus, initially the roll! is pressed against the stop I4 by the spring plunger I3 and is thereby set in correct thread-and-gap relationship for the commencement of the rolling operation. On being inserted between therolls the workpiece I2 is rolled towards the central plane (position B, B) and during the progressive formation of the thread the sliding roll 2 is moved axially on its spindle 4, due to the tracking of. its thread with that'on the work-piece, against the action of the spring plunger i3, until the rolling operation, has been completed and the work-piece leaves the rolls. The roll 2 is then returned to its stop It by the plunger I3, ready for the insertion of the next piece. At each position of the roll 2 during this axial displacement the thread-and-gap relationship between the rolls is correct at the plane through the points of contact of -the work-piece with the rolls.

I claim:

1. A machine for rolling screw threads comprising two threading rollshaving opposed peripheries spaced apart mounted to revolve at different peripheral speeds about parallel axes so as to cause a work-piece to be fed or drawn laterally between the rolls, and means for positively driving said rolls in the same direction: one of said rolls being rotatable in a fixed plane and the other one being free to slide axially relatively to the other to ensure a constantlycorrect thread relationship between the rolls throughout the movement of the Work-piece between them.

2. A machine for rolling screw-threads comprising two opposed threading rolls mounted to revolve about parallel axes at difierent peripheral speeds so as to cause a work-piece to be fed or drawn laterally between the rolls; one of said rolls being rotatable in a fixed plane and the other one being free to slide axially relatively to 'the'other; means for positively driving said 7 rolls in the same direction; and spring means for maintaining the slidable roll in an initial rolling'operation, the said slidable roll moving rolls, one roll being rigid with its spindle and the other being freely slidably on' its spindle; means for positively driving the spindles at the same rotational speed and in the same direction; and a spring acting on the slidable roll to maintain it in an initial position in which the thread-and-gap relationship between the two rolls is correct for the commencement of the rolling operation, the said slidable roll sliding axially against the action of the spring as a workpiece passes laterally between the rolls, so as to maintain a constantly-correct thread relationship between the rolls throughout the movement of the work-piece between them.

4. A'machine for rolling screw-threads comprising two spaced threading rollsone of which is free to move axially in relation to the other; means for positively driving said rolls at different peripheral speeds and in the same direction; an adjustable stop device co-operating with one end of the roll for determining its initial position; and spring means acting on said roll and tending to move it towards the stop; the said slidable roll moving away from the stop and against the action or the spring during the rolling operation due to the tracking of its thread with that on a work-piece being rolled between the rolls.

GEORGE GOULD. 

